A 66-year-old millionaire whose Monte Sereno mansion was invaded by robbers died of asphyxiation after his assailants left him gagged with packaging tape as they beat his wife and told her to "be quiet if you want to live," authorities said.

Details of the crime are contained in police affidavits unsealed Friday. They explain the arrest of four suspects in the Nov. 30 killing of Raveesh "Ravi" Kumra, a cell phone entrepreneur and the former owner of Mountain Winery in Saratoga.

Police believe Kumra was set up by a prostitute he had hired who relayed information about his 7,000-square foot home - along with photographs - to members of Oakland gangs that have invaded the homes of Asian and Indian families around the Bay Area.

The affidavits suggest that the assailants, who made off with cash, jewelry and rare coins, were foiled by DNA and modern technology.

The documents do not give a cause of death, but the Santa Clara County coroner concluded that Kumra was asphyxiated because of the tape, said prosecutor Kevin Smith. Two law enforcement sources familiar with the case said Kumra had sinus problems.

Smith declined to comment on whether the cause of death would affect the prosecution. Under California law, a death that occurs in the commission of a felony such as a robbery can still be a murder, even if the killing is not intentional.

Facing murder charges in the Monte Sereno case are Deangelo Austin, 21, Javier Garcia, 21, and 26-year-old Lukis Anderson, who each could be subject to the death penalty. Prosecutors have alleged that Austin and Garcia committed the crime for the benefit of a street gang.

The alleged prostitute, 22-year-old Raven Dixon, is accused of being an accessory to the killing, and faces a gang enhancement as well.

Attorneys for the defendants did not return calls Friday.

Early-morning terror

In the police affidavits, Monte Sereno Detective Erin Lunsford said Kumra's wife called 911 at 1:36 a.m. to report the robbery at the home on Withey Road - and that her husband appeared to be dead.

The intruders first set upon Kumra, using tape to gag him, blindfold him and tie up his hands and feet, Lunsford said. Then they woke up his wife, Harinder Kumra, hitting her in the mouth with something cold and hard, threatening her and binding her with tape as well.

Lunsford said investigators had learned that Raveesh Kumra frequently hired prostitutes - including Dixon - bringing them to his home when his wife was gone, to friends' houses or to hotels in Los Gatos.

A key break in the case, Lunsford said, came when investigators found that Dixon had plugged her cell phone into Kumra's laptop computer in April 2012 and, perhaps inadvertently, backed up the data. It contained photos of the house, including gates and fences.

'Party' offer

Meanwhile, the affidavits say, Kumra's Google Voice account revealed he had declined Dixon's offer to "party" two weeks before the robbery.

Lunsford said Austin's DNA had been found on a piece of tape near the victim's body. Anderson's DNA was found on the dead man's fingernails, she said, and Garcia's genetic material turned up on a latex glove in the kitchen sink.

According to police, Austin is a member of an Oakland gang called the Money Team that authorities have blamed for an increase in violence in that city, while Garcia is a member of an allied gang known as Ghost Town.

Dixon was close with two other prostitutes who had been with Kumra at his home and at Las Gatos hotels, Lunsford said - Austin's sister and a woman who has a brother in the Money Team.

In a police interview, Dixon denied that she was a prostitute, that she had ever met Kumra, that she had spent time in Los Gatos or Monte Sereno or that she had taken photos of the mansion.